Recently, interest in heat-resistant resins used in components requiring heat resistance, such as electrical and electronic products and interior/exterior materials of automobiles, is increasing.
Resins having superior heat resistance are prepared into latex through emulsion polymerization and then into a powder or pellet form through a coagulation step, a dehydration step, and a drying step. However, since the prepared latex has very high glass transition temperature, coagulation is not easily carried out. In addition, since the latex has a very high moisture content (50% or higher), the latex is prepared into only a fine particle form.
As an exemplary method to address such a latex coagulation problem, there is a multistage process of inducing agglomeration of particles at high temperature via a pressure-aging process, etc. However, this multistage process is very complex.
As another example, latex may be coagulated by disturbing stability of latex particles, which are stabilized by an emulsifier added during emulsion polymerization, using a chemical method, in which various coagulants are used, or using a mechanical methods, in which mechanical force, such as strong shearing force, is used. The chemical method disturbs stability using different coagulants dependent upon emulsifier types used to secure stability of latex. The mechanical method is characterized in that strong shearing force is applied to latex such that repulsive force between emulsifiers is overcome and latex particles are agglomerated.
As a chemical coagulation method, a rapid coagulation process was suggested. This method is characterized in that an aqueous coagulant solution including inorganic salt, acid, etc. is added in a large amount such that stability of an emulsifier is disturbed and thus polymers in latex are rapidly agglomerated. Such agglomeration of latex polymer particles is called coagulation and an agglomerate of polymer particles is called slurry. Since such slurry is physically, weakly bound, it is easily broken up by external shearing force by means of a stirrer, etc. Therefore, primarily coagulated slurry is subjected to an aging process wherein temperature is elevated such that chains penetrate one another and, accordingly, binding force is increased. A resultant slurry is subjected to dehydration and drying processes. Finally, the slurry is obtained in a powder form.
In the case of the rapid coagulation wherein coagulation is carried out with a large amount of a coagulant as described above, stability of latex is very rapidly disturbed, and thus, agglomeration of polymer latex particles very rapidly and disorderedly occurs. By such disordered coagulation, an apparent specific gravity is lowered and a size distribution of final particles becomes very wide.
In addition, a slow coagulation process wherein a coagulation rate is controlled by split feeding of a coagulant to improve characteristics of a powder of generated final particles was suggested. The coagulation occurs in a secondary well area in which an energy barrier is present, whereby a coagulation rate is low and rearrangement of particles may be carried out. Accordingly, it is possible to prepare spherical particles due to regular filling. However, a use amount of total coagulants used in the slow coagulation process is similar to that of the rapid coagulation and the slow coagulation process is different from the rapid coagulation only in that coagulation is carried out by split feeding. Accordingly, generation of much wastewater due to use of a large amount of coagulants cannot be avoided. In addition, in the case of a primary coagulation bath, a small amount of a coagulant is added, compared to the rapid coagulation, and thus, the viscosity of a slurry increases. Accordingly, so as to secure flowability, a large amount of water should be added, compared to the rapid coagulation. In addition, the slow coagulation process disadvantageously has a high moisture content, compared to the rapid coagulation.
Therefore, there is a need for a heat-resistant resin to increase dispersibility by improving particle size characteristics, improve coagulation characteristics, and reduce a moisture content and a method of preparing the same.